CN114669190A

CN114669190A - Catalytic article for treating exhaust gas

Info

Publication number: CN114669190A
Application number: CN202210290522.4A
Authority: CN
Inventors: J·加斯特; O·索恩塔格; T·根施欧; G·斯迈德勒; A·P·沃克尔; M·拉尔森; P·马尔卡特; L·张
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 2014-05-16
Filing date: 2015-05-15
Publication date: 2022-06-28
Anticipated expiration: 2035-05-15
Also published as: CN106457147A; US9545602B2; RU2016149400A; EP3142773B1; US20160008759A1; BR122022003711B1; GB2530129B; GB201508393D0; RU2019132210A3; DK3142773T3; RU2704800C2; GB2530129A; DE102015107647A1; WO2015175921A2; CN114669190B; JP2017522170A; BR112016026502A2; JP6634545B2; EP3466521B1; RU2019132210A

Abstract

A catalytic article is provided comprising (a) a flow-through honeycomb substrate having channel walls; (b) first NH₃-an SCR catalyst composition coated on and/or within the channel walls in the first zone; and (c) a second NH₃-an SCR catalyst composition coated on and/or within channel walls in a second zone, provided that the first zone is upstream of the second zone and the first and second zones are adjacent or at least partially overlapping; and wherein the first NH₃-SCR catalysisThe agent comprises a first copper-loaded molecular sieve having a copper to aluminum atomic ratio of about 0.1 to 0.375, and a second NH₃-the SCR catalyst comprises a second copper supported molecular sieve having a copper to aluminum atomic ratio of from about 0.3 to about 0.6.

Description

Catalytic article for treating exhaust gas

The present application is a divisional application of the invention patent application having an application date of 2015, 5/15, application number of 201580032905.X, entitled "catalytic article for treating exhaust gas".

Background

Technical Field

The present invention relates to catalytic articles and methods for treating combustion exhaust gases.

Description of related Art

The combustion of hydrocarbon-based fuels in engines produces exhaust gases containing mostly relatively non-toxic nitrogen (N)₂) Water vapor (H)₂O) and carbon dioxide (CO)₂). The exhaust gases, however, also contain relatively small proportions of harmful and/or toxic substances, such as carbon monoxide (CO) from incomplete combustion, Hydrocarbons (HC) from unburned fuel, Nitrogen Oxides (NO) from excessively high combustion temperatures_x) And particulate matter (mostly soot). In order to mitigate the environmental impact of flue gases and exhaust gases released into the atmosphere, it is desirable to eliminate or reduce the amount of undesirable components, preferably by a process that does not in turn produce other harmful or toxic substances.

Typically, the exhaust gas from a lean burn internal combustion engine has a net oxidising effect due to the high proportion of oxygen that is provided to ensure adequate combustion of the hydrocarbon fuel. In such gases, to removeOne of the most troublesome components to remove is NO_xIncluding Nitric Oxide (NO), nitrogen dioxide (NO)₂) And nitrous oxide (N)₂O). Adding NO_xReduction to N₂This is particularly problematic because the exhaust gas contains sufficient oxygen to promote the oxidation reaction rather than the reduction reaction. However, NO_xReduction may be by a process commonly referred to as Selective Catalytic Reduction (SCR). The SCR process comprises the addition of NO in the presence of a catalyst and with the aid of a reducing agent such as ammonia_xConversion to elemental nitrogen (N)₂) And water. In the SCR process, a gaseous reductant, such as ammonia, is added to the exhaust gas stream before the exhaust gas contacts the SCR catalyst. The reducing agent is adsorbed on the catalyst and NO_xThe reduction reaction occurs as the gas passes in or over the catalytic substrate. The chemical formula for the SCR reaction using the stoichiometric ratio of ammonia is:

4NO+4NH₃+O₂→4N₂+6H₂O

2NO₂+4NH₃+O₂→3N₂+6H₂O

NO+NO₂+2NH₃→2N₂+3H₂O

zeolites with exchanged transition metals are known to be useful as SCR catalysts. Conventional copper exchanged small pore zeolites are particularly useful for achieving high NO at low temperatures_xAnd (4) conversion rate. However, NH₃Interaction with NO adsorbed on the transition metal of the exchanged zeolite can lead to undesirable side reactions that produce N₂And O. The N is₂O is particularly difficult to remove from the exhaust stream. Thus, there is still a need to obtain high NO_xConversion and minimal production of N₂An improved process for O. The present invention particularly addresses this need.

Disclosure of Invention

Applicants have discovered that having at least two catalytic zones, each comprising a catalytic substrate comprising a copper-supported molecular sieve, can significantly reduce undesirable N₂Production of O while maintaining an overall high N in the SCR reaction₂Selectivity provided that the Cu to Al molar ratio of the copper-supported molecular sieve catalyst located in the upstream zone is less thanCopper-loaded molecular sieves in the downstream zone. E.g. high N₂Selectivity and low N₂The O by-product can be achieved in the SCR process by passing the exhaust gas in or on a substrate having upstream NH containing a copper loaded molecular sieve having a Cu to Al molar ratio of about 0.1 to 0.375₃-SCR catalyst zone and downstream NH with Cu to Al molar ratio of about 0.3 to 0.6₃-an SCR catalyst zone. In a preferred embodiment, the upstream molecular sieve has a higher silica to alumina (SAR) ratio than the downstream molecular sieve. In another preferred embodiment, the upstream molecular sieve catalyst has a lower copper loading than the downstream molecular sieve catalyst. In yet another preferred embodiment, the upstream molecular sieve catalyst has a higher SAR and a lower copper loading than the downstream molecular sieve catalyst.

Accordingly, in one aspect, a catalytic article is provided comprising (a) a flow-through honeycomb substrate having an inlet side, an outlet side, an axial length from the inlet side to the outlet side, and a plurality of channels defined by channel walls extending from the inlet side to the outlet side; (b) first NH₃-an SCR catalyst composition coated on and/or within the channel walls in the first zone; and (c) a second NH₃-an SCR catalyst composition coated on and/or within the channel walls in a second zone, provided that the first zone is upstream of the second zone, and the first and second zones are in series; and further with the proviso that the first NH₃-the SCR catalyst comprises a first copper-supported molecular sieve having a molar ratio of copper to aluminum of about 0.1 to 0.375, and a second NH₃-the SCR catalyst comprises a second copper-supported molecular sieve having a molar ratio of copper to aluminum of about 0.3 to about 0.6.

In another aspect, a catalyst article is provided comprising (a) a flow-through honeycomb substrate having an inlet side, an outlet side, an axial length from the inlet side to the outlet side, and a plurality of channels defined by channel walls extending from the inlet side to the outlet side; (b) a first catalytic zone consisting of a first support coating (washcoat); (c) a second catalytic zone consisting of a first washcoat and a second washcoat; (d) a third catalytic zone consisting of a second washcoat; and (e) a fourth catalytic zone consisting of the second washcoat layer on the third washcoat layer; wherein the first washcoat layer comprises a first copper-supported molecular sieve, the second washcoat layer comprises a second copper-supported molecular sieve, wherein the first and second molecular sieves are different materials, and the third washcoat layer comprises an ammonia oxidation catalyst, and wherein the first, second, third, and fourth zones are arranged in series on the substrate, each zone being adjacent to the next zone in the series, the first zone being closest to the inlet side, and the fourth zone being closest to the outlet side.

In yet another aspect of the present invention, a system for treating exhaust gas is provided, comprising: (a) a catalytic article as described herein; and (b) is selected from DOC, NAC, external NH₃One or more exhaust treatment components of an injector, a two-stage SCR catalyst, an ASC, and a particulate filter, wherein the catalytic article of claim 1 and the one or more exhaust treatment components are in fluid communication and are in series.

In another aspect of the present invention, there is provided a method of treating exhaust gas, comprising: (a) so as to contain NO_xAnd NH₃With the catalytic article of claim 1; and (b) reacting NO_xIs selectively reduced to N₂And H₂O。

In some embodiments, the present invention relates to the following items:

1. a catalytic article, comprising:

a. a flow-through honeycomb substrate having an inlet side, an outlet side, an axial length from the inlet side to the outlet side, and a plurality of channels defined by channel walls extending from the inlet side to the outlet side;

b. first NH₃-an SCR catalyst composition coated on and/or within the channel walls in the first zone; and

c. second NH₃-an SCR catalyst composition coated on and/or within channel walls in a second zone, provided that the first zone is upstream of the second zone and the first and second zones are adjacent or at least partially overlapping;

wherein the first NH₃-SCR catalystA first copper-loaded molecular sieve comprising a copper to aluminum atomic ratio of about 0.1 to 0.375, and a second NH₃-the SCR catalyst comprises a second copper-supported molecular sieve having a copper to aluminum atomic ratio of from about 0.3 to about 0.6.

2. The catalytic article of item 1, wherein the first zone is adjacent to the second zone.

3. The catalytic article of item 1, wherein the first zone completely overlaps the second zone.

4. The catalytic article of clause 1, wherein the first zone extends from the inlet side to a first endpoint that is at a location that is about 10-40% of the axial length, and wherein the second zone is about 20-90% of the axial length, provided that the first and second zones are adjacent or overlap by less than 90% of the axial length.

5. The catalytic article of clause 4, wherein the first zone overlaps the second zone.

6. The catalytic article of clause 4, wherein the second zone overlaps the first zone.

7. The catalytic article of clause 1, wherein the first copper-supported molecular sieve has a lower copper concentration than the second copper-supported molecular sieve.

8. The catalyst article of clause 2, wherein the first copper-supported molecular sieve has a copper loading of about 50-90% of the second copper-supported molecular sieve.

9. The catalytic article of clause 1, wherein the first copper-supported molecular sieve has a first SAR and the second copper-supported molecular sieve has a second SAR that is greater than the first SAR.

10. The catalyst article of clause 9, wherein the first molecular sieve is an aluminosilicate having a SAR of about 10 to about 20 and the second molecular sieve is an aluminosilicate having a SAR of about 20 to about 50.

11. The catalyst article of clause 9, wherein the first and second molecular sieves have a small pore framework.

12. The catalyst article of clause 9, wherein the first and second molecular sieves have a CHA framework.

13. The catalyst article of clause 9, wherein the first molecular sieve is a silicoaluminophosphate and the second molecular sieve is an aluminosilicate having a SAR of about 15 to about 50.

14. The catalyst article of clause 4, wherein the first and second zones overlap to create a third catalyst zone, wherein the third zone has a higher copper content than the individual first and second zones.

15. The catalyst article of item 1, further comprising an ASC zone having an ammonia oxidation catalyst coated on and/or within the channel walls, wherein the ASC zone extends from the outlet side to a distance of about 10-50% of the axial length and does not contact the first zone.

16. The catalyst article of clause 15, wherein the second NH₃-the SCR catalyst composition completely overlaps the oxidation catalyst.

17. The catalyst article of clause 16, wherein the oxidation catalyst comprises platinum.

18. A catalyst article, comprising:

a. a flow-through honeycomb substrate having an inlet side, an outlet side, an axial length from the inlet side to the outlet side, and a plurality of channels defined by channel walls extending from the inlet side to the outlet side,

b. a first catalytic zone consisting of a first washcoat,

c. a second catalytic zone consisting of a first washcoat and a second washcoat,

d. a third catalytic zone consisting of a second washcoat layer, and

e. a fourth catalytic zone consisting of the second washcoat layer on the third washcoat layer,

wherein the first washcoat layer comprises a first copper-supported molecular sieve, the second washcoat layer comprises a second copper-supported molecular sieve, wherein the first and second molecular sieves are different materials, and the third washcoat layer comprises an ammonia oxidation catalyst, and

wherein first, second, third and fourth zones are arranged in series on the substrate, each zone being adjacent to the next zone in the series, the first zone being closest to the inlet side and the fourth zone being closest to the outlet side.

19. A system for treating an exhaust gas, comprising:

a. the catalytic article of item 1; and

b. selected from DOC, NAC, external NH₃One or more exhaust treatment components of an injector, a two-stage SCR catalyst, an ASC, and a particulate filter,

wherein the catalytic article of item 1 and the one or more exhaust treatment components are in fluid communication and are in series.

20. A method for treating exhaust gas, comprising:

so as to contain NO_xAnd NH₃Contacting the exhaust gas of item 1 with a catalytic article according to item 1;

adding NO_xIs selectively reduced to N₂And H₂O。

Drawings

FIG. 1 is a diagram showing one embodiment of the present invention with an arrangement of zoned SCR catalysts;

FIG. 2 is a diagram showing an embodiment of the invention with another arrangement of zoned SCR catalysts;

FIG. 3 is a diagram showing an embodiment of the invention with another arrangement of zoned SCR catalysts;

FIG. 4 is a diagram showing an embodiment of the invention with another arrangement of zoned SCR catalysts;

FIG. 4A is a diagram showing an embodiment of the invention with another arrangement of zoned SCR catalyst;

FIG. 5 is a diagram showing an embodiment of the present invention with an arrangement of zoned SCR catalyst and ammonia oxidation catalyst;

FIG. 6 is a diagram showing another arrangement of a zoned SCR catalyst according to an embodiment of the present invention;

FIG. 7 is a diagram showing an embodiment of the invention with another arrangement of a zoned SCR catalyst comprising two substrates;

FIG. 7A is a diagram showing an embodiment of the invention with another arrangement of a zoned SCR catalyst comprising two substrates and an ASC zone;

FIG. 8 is a diagram showing an embodiment of the present invention with another arrangement of zoned SCR catalysts, where one of the zones is an extruded catalyst body;

FIG. 8A is a diagram showing an embodiment of the invention with another arrangement of zoned SCR catalyst where one of the zones is an extruded catalyst body;

FIG. 8B is a diagram showing an embodiment of the invention with another arrangement of zoned SCR catalyst where the zones are on an extruded catalyst body;

FIG. 9 is a diagram showing an embodiment of the present invention with another arrangement of zoned SCR catalysts, where one of the zones is an extruded catalyst body;

FIG. 10 is a diagram of a flow-through honeycomb substrate comprising a zoned SCR catalyst;

FIG. 10A is a diagram of cells of a flow-through honeycomb substrate; and

FIG. 11 is a diagram of a system for treating exhaust gas according to one embodiment of the present invention.

Detailed Description

The present invention relates at least in part to a method for improving ambient air quality, particularly for treating exhaust gas emissions produced by power plants, gas turbines, lean-burn internal combustion engines, and the like. Exhaust emissions are at least partially reduced by reducing NO over a wide operating temperature range_xThe concentration is improved. NO (nitric oxide)_xIs accomplished by passing the exhaust gas in or on a substrate, preferably a honeycomb flow-through monolith, having two or more NH's disposed in a zone₃-an SCR catalyst.

Preferably, the first NH₃-an SCR catalyst composition coated on and/or within channel walls in a first zone of a flow-through monolith, and a second NH₃-the SCR catalyst composition is coated on and/or within channel walls in a second zone of the flow-through monolith, the first zone being upstream of the second zone. In certain embodiments, the first or second zone may be in the form of an extruded catalyst body and the other zone is a coating on the body. In certain embodiments, the first region and the second regionThe zones are of the same catalyst formulation, provided that the washcoat loading in the first zone is lower than in the second zone. In one example, the washcoat loading of the first zone may be 85%, 75%, 65%, or 50% of the post washcoat loading. In certain embodiments, the first and second zones have the same catalyst formulation, but different washcoat loadings, respectively, on different substrates. Preferably, the two substrates are adjacent to each other. In certain embodiments, the substrates are located in an exhaust gas treatment system such that no other SCR catalyst, preferably no other exhaust treatment catalyst, is present between the two substrates.

Referring to fig. 1, an embodiment of the invention is shown wherein a flow-through honeycomb substrate 10 has a first catalyst zone 20 and a second catalyst zone 30, wherein the first and second catalyst zones are continuous and in contact. The terms "first region" and "second region" refer to the orientation of the regions on the substrate. More specifically, the zones are oriented in series such that under normal operating conditions, the exhaust gas to be treated contacts the first zone before contacting the second zone. In one embodiment, the first and second zones are arranged in series such that one is immediately adjacent the other without interruption (i.e., there is no catalyst or other exhaust treatment operation, such as a filter, between the first and second zones). Thus, in certain embodiments, the first zone is upstream of the second zone relative to a normal exhaust flow 1 in or on the substrate.

The difference in catalyst material of the first and second zones produces different treatment of the exhaust gas as it passes in or on the substrate. For example, the first zone selectively reduces NO_xWhile producing a lower N than the second region₂O by-product, and the second zone selectively reduces NO with a higher selectivity than the first zone_x. The synergistic effect of the combination of the two zones improves the overall performance of the catalyst as compared to a single catalyst system or other zoned arrangement.

In fig. 10, a zoned catalytic substrate 2 is shown, wherein the substrate is a honeycomb flow-through monolith 100 having an inlet side 110 and an outlet side 120 relative to the normal direction of exhaust gas flow 1 through the substrate. The substrate has an axial length 190 that extends from the inlet side 110 to the outlet side 120. Fig. 11 shows a single cell 200 of a honeycomb substrate having channel walls 110, the channel walls 110 defining open channels 120 through which exhaust gas can flow. The channel walls are preferably porous or semi-porous. The catalyst of each zone may be a coating on the surface of the wall, a coating partially or completely penetrating into the wall, introduced directly into the wall as an extrudate, or some combination thereof.

In FIG. 1, the first zone 20 extends from the inlet side 110 to a first end 29, the first end 29 being located about 10-90%, such as about 80-90%, about 10-25%, or about 20-30% of the axial length 190. The second zone 120 extends from the outlet side 120 to about 20 to 90 percent, such as about 60 to about 80 percent or about 50 to about 75 percent, of the axial length 190. Preferably, the second region extends to at least the first end point such that the first and second regions are in contact. The axial length is preferably less than 24 inches, such as from about 1 to about 24 inches, from about 3 to about 12 inches, or from about 3 to about 6 inches.

In fig. 2, the first catalyst zone 20 partially overlaps the second catalyst zone 30. In fig. 3, the second catalyst area 30 partially overlaps the first catalyst area 20. The overlap is preferably less than 90% of the axial length of the substrate, for example from about 80 to about 90%, less than about 40%, from about 40 to about 60%, from about 10 to about 15%, or from about 10 to about 25%. For embodiments in which the second catalyst region overlaps the first catalyst region, the overlap may be greater than 50% of the axial length, for example 80-90%. For embodiments in which the first catalyst zone overlaps the second catalyst zone, the overlap is preferably less than 50% of the axial length, for example about 10-20%.

In fig. 4, the first catalyst zone 20 completely overlaps the second catalyst zone 30. Preferably, the first and second regions are in contact (i.e. there is no intervening catalytically active layer between the first and second regions). For such embodiments, the exhaust gas to be treated first contacts the first zone and is at least partially treated by the first zone. At least a portion of the exhaust gas permeates the first zone where it contacts the second zone where it is subsequently treated in the second zone. At least a portion of the treated exhaust gas permeates back into the first zone, into the open channels, and out of the substrate. Fig. 4 shows an embodiment in which the first and second catalyst zones extend the entire axial length of the substrate. Fig. 4A shows an embodiment in which the first catalyst zone completely overlaps the second zone, the first catalyst zone extends the entire axial length of the substrate, and the second zone extends less than the entire axial length of the substrate from the outlet side.

Fig. 5 shows another embodiment of the present invention. Here, the catalytic article further comprises a third catalyst zone proximate to and preferably extending to the outlet side of the substrate. The third catalyst zone comprises an oxidation catalyst, preferably a catalyst effective for oxidizing ammonia. In certain embodiments, the catalyst comprises one or more Platinum Group Metals (PGM), such as Pt, Pd, or combinations thereof, preferably on a metal oxide support, such as alumina. The combination of the second and third zones arranged in layers acts as an ammonia slip catalyst, wherein at least a portion of the excess ammonia not consumed by the upstream SCR reaction passes through the second zone to the third zone where it is oxidized to H₂O and Secondary NO_x。 H₂O and Secondary NO_xBack through the second zone where secondary NO_xIs reduced to N via an SCR type reaction₂And H₂O。

Another embodiment of the invention is shown in fig. 6, where the substrate supports four discrete catalyst zones, each of which contains a separate catalyst composition. The compositions of the first, second and third catalyst zones are similar to those described above. The fourth catalyst zone is located between the first and second zones such that the first, fourth and second zones are in series, the first zone contacting the fourth zone, and the fourth zone contacting the second zone. In certain embodiments, the fourth zone may have two or more catalyst layers, wherein each catalyst layer comprises a copper-supported molecular sieve.

The total amount of copper per linear inch in the fourth zone is greater than the total amount of copper per linear inch in the first zone and less than the second zone, or greater than the total amount of copper per linear inch in the individual first and second zones. In certain embodiments, the molecular sieve of the fourth zone is the same as the molecular sieve of the first zone and/or the second zone. In certain embodiments, the molecular sieve of the fourth zone comprises two molecular sieve materials. For example, the fourth zone may comprise the molecular sieve of the first zone and the molecular sieve of the second zone, provided that the first and second zones have different molecular sieves.

Preferably, the first and second zones are arranged consecutively on a single substrate such that the first zone contacts the second zone. In certain embodiments, the first and second zones are disposed on separate substrates located in the exhaust treatment system such that the first and second zones are in series and contact. The two substrates may be the same or different substrates. For example, the first substrate may have a higher porosity than the second substrate, the first and second substrates may be of different compositions or have different cell densities, and/or the first and second substrates may be of different lengths. In FIG. 7, the first and second zones are arranged on separate substrates located in the exhaust treatment system such that the first and second zones are in series and adjacent, but not in direct contact. The maximum distance between the first and second substrates is preferably less than 2 inches, more preferably less than 1 inch, and preferably there is no intervening substrate, filter or catalyst material between the first and second zones and/or between the first and second substrates. In fig. 7A, the second substrate further comprises an underlying layer of ammonia oxidation catalyst 40 extending from the outlet side of the substrate to a length less than the total length of the substrate. The second zone completely covers the oxidation catalyst and preferably extends the length of the substrate.

In certain embodiments, the first or second catalyst zone comprises extruded catalyst material. The embodiment shown in fig. 8, for example, comprises a first catalytic zone 26 in the form of a coating on and/or within a portion of an extruded catalyst substrate. The extruded catalyst substrate in turn comprises a second catalytic zone 16. The first zone is arranged on the substrate such that it is upstream of the second zone with respect to the normal flow of the exhaust gas 1. The catalytically active substrate in zone 16 comprises catalytically active material similar to the other second zones described herein. In fig. 8, the first zone extends from the inlet side to less than the entire length of the substrate. In fig. 8A, the first zone 26 completely covers the catalytically active substrate comprising the second zone.

In FIG. 8B, a catalytically active substrate 300, such as a flow-through honeycomb substrate coating formed from an extruded catalytic materialCovered by an upstream zone 310 and a downstream zone 330. The upstream zone extends from the inlet side 312 to a first end point 314 that is located about 10-80%, such as about 50-80%, about 10-25%, or about 20-30% of the axial length 390. The downstream region extends from the outlet side 344 to the second end 332 and is located about 20-80%, such as about 20-40%, about 60-about 80%, or about 50-about 75% of the axial length 390. The upstream and downstream regions are not in direct contact, and therefore a gap 320 exists between the upstream and downstream regions. Preferably, this gap does not contain a catalyst layer, but is instead exposed directly to the exhaust gas to be treated. The exhaust gases contacting the catalyst body at the gap, thereby treating the exhaust gases, e.g. selectively reducing NO in the exhaust gases_xA part of (a). The gap defined by first end 314 and second end 332 is preferably less than 75% of the axial length, such as from about 40 to about 60, from about 10 to about 15%, or from about 10 to about 25% of the axial length 390. Optionally NH₃The oxidation catalyst is coated on and/or within the substrate 300 in a zone extending from the outlet side 344 toward the inlet side 312 to a length equal to or less than the length of the downstream zone. Optionally NH₃The oxidation catalyst is preferably a washcoat which is completely covered by the catalyst composition forming the downstream zone.

There are no particular restrictions on the composition of the catalyst in the upstream, extrudate, and downstream zones, and the conditions are such that at least two of the upstream, extrudate, and downstream zones meet the requirements of the first and second zones as defined herein, i.e., the Cu to Al ratio of the copper-supported molecular sieve in the first zone is less than the Cu to Al ratio of the copper-supported molecular sieve in the second zone. In one example, the upstream zone corresponds to the first zone, and the downstream zone corresponds to the second zone. In such embodiments, the extruded catalyst body preferably comprises another type of SCR catalyst, such as vanadium, preferably supported on a metal oxide such as TiO₂And optionally one or more additional metals such as tungsten. In another example, the extruded catalyst body corresponds to a first zone and the downstream zone corresponds to a second zone. In this example, the upstream zone may comprise another type of catalyst, preferably an SCR catalyst such as an iron-supported molecular sieve. In another example, the upstream zone corresponds to the first zone and the extrudate corresponds to the second zone. At this pointIn an example, the downstream zone may comprise another, preferably another type of SCR catalyst, such as one of those described herein.

Fig. 9 shows another embodiment, wherein the first catalytic zone 17 is part of an extruded catalytic body and the second catalyst zone 37 is a coating on and/or within a portion of an extruded catalyst substrate. Also, the first zone is disposed upstream of the second zone with respect to the normal flow of exhaust gas 1, and the catalytically active substrate in zone 17 comprises catalytically active material similar to the material of the other first zones described herein.

The first catalytic zone comprises a first NH₃-an SCR catalyst composition. First NH₃SCR catalysts comprise copper-supported molecular sieves as catalytically active component, but may comprise other components, in particular non-catalytically active components such as binders. As used herein, a "catalytically active" component is directly involved in NO_xCatalytic reduction and/or NH of₃Or other nitrogen-based SCR reductant. Accordingly, the "non-catalytically active" component is not directly involved in NO_xCatalytic reduction and/or NH of₃Or other nitrogen-based SCR reductant.

Useful molecular sieves are crystalline or crystal-like materials, which may be, for example, aluminosilicates (zeolites) Or Silicoaluminophosphates (SAPOs). Such molecular sieves are made of repetitive SiO₄、AlO₄And optionally PO₄Tetrahedral units are connected together, for example in a ring, to build a framework with regular intra-crystalline hole and molecular size channels. The specific arrangement of tetrahedral units (ring members) creates a framework for the molecular sieve, and according to convention, each unique framework is assigned a unique three-letter code (e.g., "CHA") by the International Zeolite Association (IZA). Examples of useful molecular sieve frameworks include macroporous frameworks (i.e., having a minimum ring size of 12 members), mesoporous frameworks (i.e., having a minimum ring size of 10 members), and small pore frameworks (i.e., having a minimum ring size of 8 members). Examples of frameworks include BEA, MFI, CHA, AEI, LEV, KFI, MER, RHO, ERI, OFF, FER, and AFX. The molecular sieve may also be a co-framework of two or more frameworks, e.g. AEI and CHAA living body. In certain embodiments, the first and/or second zone may independently comprise a blend of two or more molecular sieves. Preferred blends have at least one molecular sieve having a CHA framework, and more preferably a majority of the CHA framework.

Particularly useful molecular sieves are small pore zeolites. As used herein, the term "small pore zeolite" means a zeolite framework having a maximum ring size of 8 tetrahedral atoms. Preferably, the main crystalline phase of the molecular sieve is comprised of one or more small pore frameworks, although other molecular sieve crystalline phases may also be present. Preferably, the primary crystalline phase comprises at least about 90 wt%, more preferably at least about 95 wt%, and even more preferably at least about 98 or at least about 99 wt% of the small pore molecular sieve framework, based on the total weight of the molecular sieve material.

In some examples, the small pore zeolites used in the present invention have a pore size in at least one dimension that is less than

In one embodiment, the small pore zeolite has a framework selected from the group consisting of: ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, and ZON. Preferred zeolite frameworks are selected from AEI, AFT, AFX, CHA, DDR, ERI, LEV, KFI, RHO, and UEI. For certain applications, the preferred zeolite framework is selected from AEI, AFT and AFX, particularly AEI. In certain applications, the preferred zeolite framework is CHA. In certain applications, the ERI backbone is preferred. Specific zeolites that may be used in the present invention include SSZ-39, Mu-10, SSZ-16, SSZ-13, Sigma-1, ZSM-34, NU-3, ZK-5 and MU-18. Other useful molecular sieves include SAPO-34 and SAPO-18. In a particularly preferred embodiment, the first and second NH groups₃-the SCR catalyst independently comprises an aluminosilicate having a CHA framework loaded with copper (e.g. SSZ-13). In a further particularly preferred embodiment, the first NH₃-the SCR catalyst comprises a copper supported SAPO-34 molecular sieve, and a secondNH₃-the SCR catalyst comprises a copper supported aluminosilicate having the CHA framework.

Preferred aluminosilicates have a silica to alumina ratio (SAR) of about 10 to about 50, such as about 15 to about 30, about 10 to about 15, 15 to about 20, about 20 to about 25, about 15 to about 18, or about 20 to about 30. Preferred SAPOs have a SAR less than 2, such as from about 0.1 to about 1.5, or from about 0.5 to about 1.0. The SAR of a molecular sieve can be determined by conventional analysis. This ratio is intended to represent as closely as possible the ratio in the hard atomic framework of the molecular sieve crystal and does not include cations or other forms of silicon or aluminum in the binder or within the channels. Because it is difficult to directly measure the SAR of a molecular sieve after combination with a binder material, particularly an alumina binder, the SAR values described herein are expressed in terms of the SAR of the molecular sieve itself, i.e., prior to combining the zeolite with other catalyst components.

In certain applications, the SAR of the molecular sieve in the first zone is less than the SAR of the molecular sieve in the second zone. For example, the first region molecular sieve may be an aluminosilicate having a SAR of about 10 to about 20, and the second region molecular sieve may be an aluminosilicate having a SAR of about 20 to about 50. In another example, the first region molecular sieve may be an aluminosilicate having a SAR of about 15 to about 20, and the second region molecular sieve may be an aluminosilicate having a SAR of about 25 to about 30. In another example, the first zone molecular sieve is a SAPO and the second zone molecular sieve is an aluminosilicate. In other embodiments, the first zone molecular sieves and the second zone molecular sieves have the same SAR, provided that the copper loading on the first zone molecular sieves is higher than the copper loading on the second zone molecular sieves.

The molecular sieve may comprise a framework metal other than aluminum (i.e., a metal-substituted zeolite). As used herein, the term "metal substituted" in reference to a molecular sieve refers to a molecular sieve framework in which one or more aluminum or silicon framework atoms have been replaced with a replacement metal. Conversely, the term "metal-exchanged" refers to a molecular sieve in which one or more ionic species (e.g., H) are associated with the zeolite⁺、 NH4⁺、Na⁺Etc.) have been substituted with a metal (e.g., a metal ion or free metal, such as a metal oxide), wherein the metal does not act as a molecular sieveFramework atoms (e.g., T-atoms) are introduced and instead are introduced into the molecular pores or on the outer surface of the molecular sieve framework. The exchanged metal is of the "extra-framework metal" type, which is a metal present within the molecular sieve and/or on at least a portion of the surface of the molecular sieve, preferably as an ionic species, excluding aluminum, and excluding the atoms that make up the framework of the molecular sieve. The term "metal-supported molecular sieve" means a molecular sieve comprising one or more extra-framework metals. As used herein, the terms "aluminosilicate" and "silicoaluminophosphate" do not include metal substituted molecular sieves.

The copper-supported molecular sieves of the invention comprise copper as an extra-framework metal on and/or within the molecular sieve material. Preferably, the presence and concentration of copper facilitates the treatment of exhaust gases, such as exhaust gases from diesel engines, including, for example, NO_xReduction, NH₃Oxidation and NO_xMethod of storing while also suppressing N₂And forming O.

Copper (Cu) is present in an amount relative to the amount of aluminum (Al), i.e., framework aluminum, in the molecular sieve. The Cu to Al ratio is based on the relative molar amount of copper to molar framework Al in the molecular sieve. The copper to aluminum molar ratio (Cu: Al ratio) of the copper-supported molecular sieve in the first zone is less than the Cu: Al ratio of the copper-supported molecular sieve in the second zone. Applicants have surprisingly found that adjusting the Cu to Al ratio of a molecular sieve between the upstream and downstream zones of a flow-through honeycomb substrate provides high NO in an SCR process_xConversion (especially NO and NO)₂) And N₂Selectivity while significantly reducing the undesirable N co-produced as a by-product₂The amount of O. The difference in Cu to Al ratio in the upstream catalytic zone compared to the downstream catalytic zone can be achieved as follows: loading the molecular sieve with less copper in the upstream zone than in the downstream zone, increasing the SAR of the molecular sieve in the downstream zone than the molecular sieve in the upstream zone, or a combination thereof.

Unless otherwise specified, the amount of copper supported on the molecular sieve and the concentration of copper in the catalyst are expressed in terms of copper based on the total weight of the corresponding molecular sieve, and thus are independent of the loading of the catalyst washcoat on the substrate or the presence of other materials in the catalyst washcoat.

For certain applications, the catalyst in the first zone has a Cu to Al ratio of from about 0.1 to about 0.375 and the catalyst in the second zone has a Cu to Al ratio of from about 0.3 to about 0.6, provided that the Cu to Al ratio of the catalyst in the first zone is less than the Cu to Al ratio of the catalyst in the second zone. In certain embodiments, the first zone comprises a copper-supported SAPO, and the Cu to Al ratio is about 0.01 to about 0.1. In certain embodiments, the first region comprises an aluminosilicate and the Cu to Al ratio is about 0.15 to about 0.375. In certain embodiments, the first zone comprises a SAPO and the second zone comprises an aluminosilicate molecular sieve, wherein the SAPO and aluminosilicate molecular sieves are loaded with a substantial amount of copper. In another embodiment, the molecular sieves of both the first and second regions are aluminosilicates having comparable SAR, provided that the molecular sieves of the first region are loaded with a lower concentration of copper than the molecular sieves of the second region. In another embodiment, the molecular sieves of both the first and second regions are aluminosilicates, wherein the aluminosilicates of the first region have a lower SAR than the molecular sieves of the second region, and both aluminosilicates have the same copper loading, or the molecular sieves of the first region have a lower copper loading than the molecular sieves of the second region.

In certain embodiments, extra-framework copper is present in the molecular sieve of the first or second zone at a concentration of about 0.1 to about 10 weight percent (wt%), based on the total weight of the molecular sieve, for example, about 0.5 wt% to about 5 wt%, about 0.5 to about 1 wt%, about 1 to about 5 wt%, about 2.5 wt% to about 3.5 wt%, and about 3 wt% to about 3.5 wt%.

In addition to copper, the molecular sieve may further comprise one or more additional extra-framework metals, provided that the additional extra-framework metals are present in small amounts relative to copper (i.e., the extra-framework metals are present in small amounts relative to copper)<50 mol%, for example about 1-30 mol%, about 1-10 mol%, or about 1-5 mol%). The additional extra-framework metal may be any of the well-known molecular sieve catalytically active metals used in the catalyst industry to form metal exchanges, particularly those metals known to be catalytically active for treating exhaust gases from combustion processes. Particularly preferably for NO_xReduction and storage of the metal of the process. Examples of such metals include the metals nickel, zinc, iron, tungsten, molybdenum, cobalt, titanium, zirconium, manganese, chromium, vanadium, niobium andtin, bismuth and antimony; platinum group metals such as ruthenium, rhodium, palladium, indium, platinum, and noble metals such as gold and silver. Preferred transition metals are base metals, and preferred base metals include those selected from chromium, manganese, iron, cobalt, nickel, and mixtures thereof.

Preferably, the copper is highly dispersed within the molecular sieve crystal, preferably without high temperature treatment of the metal-loaded molecular sieve. For embodiments using copper, the copper loading is preferably fully ion exchanged and/or preferably less than can be accommodated by the exchange sites of the molecular sieve support. Preferably, the catalyst is free or substantially free of substantial copper oxide, free or substantially free of copper species on the outer molecular sieve crystal surface, and/or free or substantially free of copper metal clusters, as measured by sequential thermal reduction (TPR) analysis and/or UV-visible light analysis.

In one example, the metal exchanged molecular sieve is prepared by contacting a molecular sieve, such as an H-type molecular sieve or NH₄The type molecular sieve is produced by mixing into a solution containing a soluble precursor of the catalytically active metal. The pH of the solution may be adjusted to cause precipitation of the catalytically active metal cations on or within the molecular sieve structure (but not including the molecular sieve framework). For example, in a preferred embodiment, the molecular sieve material is immersed in a solution containing copper nitrate or acetate for a sufficient time to allow catalytically active copper cations to be incorporated into the molecular sieve structure by ion exchange. The non-exchanged copper ions precipitate out. Depending on the application, a portion of the non-exchanged ions may remain in the molecular sieve material as free copper. The metal exchanged molecular sieve may then be washed, dried and calcined. The calcined material may contain a percentage of copper, expressed as copper oxide, that is present on the surface of the molecular sieve or within the cavities of the molecular sieve.

Generally, ion exchange of the catalytic metal cations into or onto the molecular sieve can be carried out at room temperature or at a temperature of up to about 80 ℃ at a pH of about 7 for a period of about 1 to 24 hours. The resulting catalytic molecular sieve material is preferably dried at about 100 ℃ and 120 ℃ overnight and calcined at a temperature of at least about 500 ℃.

In certain embodiments, the catalyst composition comprises a combination of copper and at least one alkali or alkaline earth metal, wherein the copper and alkali or alkaline earth metal are located on or within the molecular sieve material. The alkali or alkaline earth metal may be selected from sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, or some combination thereof. As used herein, the phrase "alkali metal or alkaline earth metal" does not mean that alkali metal and alkaline earth metal are used in the alternative, but that one or more alkali metals may be used alone or in combination with one or more alkaline earth metals, and one or more alkaline earth metals may be used alone or in combination with one or more alkali metals. In certain embodiments, alkali metals are preferred. In certain embodiments, alkaline earth metals are preferred. Preferred alkali or alkaline earth metals include calcium, potassium, and combinations thereof.

In certain embodiments, the catalyst composition is substantially free of magnesium and/or barium. In certain embodiments, the catalyst is substantially free of any alkali or alkaline earth metal other than calcium and potassium. In certain embodiments, the catalyst is substantially free of any alkali or alkaline earth metal other than calcium. In certain other embodiments, the catalyst is substantially free of any alkali or alkaline earth metal other than potassium. As used herein, the term "substantially free" means that the material does not have a perceptible amount of the particular metal. I.e. the presence of a particular metal in an amount that does not affect the basic physical and/or chemical properties of the material, particularly with respect to the selective reduction or storage of NO in the material_xThe ability of the cell to perform. In certain embodiments, the molecular sieve material has an alkali metal content of less than 3 wt.%, more preferably less than 1 wt.%, and even more preferably less than 0.1 wt.%.

In certain embodiments, alkali and/or alkaline earth metals (collectively referred to as a)_M) Is present in the molecular sieve material in an amount relative to the amount of copper in the molecular sieve. Preferably, Cu and A_MIn a molar ratio of about 15:1 to about 1:1, such as about 10:1 to about 2:1, about 10:1 to about 3:1, or about 6:1 to about 4:1, respectively, especially A_MIs calcium. In certain embodiments including alkali and/or alkaline earth metals, such as calcium, copper is present in an amount less than 2.5 wt.%, such as less than 2 wt.%, or less than1 wt% based on the weight of the molecular sieve. In certain embodiments, the copper-loaded molecular sieve of the second zone comprises an alkali metal or alkaline earth metal, particularly calcium, and the copper-loaded molecular sieve of the first zone is substantially free of alkali metal or alkaline earth metal. For such embodiments, copper and alkali and/or alkaline earth metal (A) are present in the molecular sieve material of the second zone_M) Is relative to the amount of aluminum in the molecular sieve, i.e., framework aluminum. As used herein, (Cu + A)_M) The ratio of Al is based on Cu + A in the corresponding molecular sieve_MRelative molar amount to molar framework Al. In certain embodiments, (Cu + A) of the molecular sieve of the second zone_M) Al in a ratio of not more than about 0.6, especially in A_MIn the case of calcium. In certain embodiments, (Cu + A)_M) The ratio of Al is at least 0.3, such as about 0.3 to about 0.6. In such embodiments, the ratio of Cu to Al of the catalyst in the first zone is from about 0.1 to about 0.375, provided that the ratio of Cu to Al in the first zone catalyst is less than (Cu + a) in the second zone catalyst_M) The ratio of Al.

In certain embodiments, copper and alkali and/or alkaline earth metal (A)_M) Is present in the molecular sieve material of the second zone in an amount relative to the amount of aluminum, i.e., framework aluminum, in the molecular sieve. As used herein, (Cu + A)_M) The ratio of Al is based on Cu + A in the corresponding molecular sieve_MRelative molar amount to molar framework Al. In certain embodiments, (Cu + A) of the catalyst material_M) The ratio of Al is not greater than about 0.6. In certain embodiments, (Cu + A)_M) The ratio of Al is not greater than 0.5, such as from about 0.05 to about 0.5, from about 0.1 to about 0.4, or from about 0.1 to about 0.2.

The alkali/alkaline earth metal may be added to the molecular sieve via any known technique, such as ion exchange, impregnation, isomorphous substitution, and the like. Copper and alkali or alkaline earth metal can be added to the molecular sieve material in any order (e.g., the metal can be exchanged before, after, or simultaneously with the alkali or alkaline earth metal), but preferably the alkali or alkaline earth metal is added before or simultaneously with the copper.

The catalytic articles of the present invention are suitable for use in heterogeneously catalyzed reaction systems (i.e., solid catalysts in contact with gaseous reactants). To improve contact surface area, mechanical stability, and/or fluid flow characteristics, an SCR catalyst is disposed on and/or within a substrate, such as a honeycomb cordierite block. In certain embodiments, one or more of the catalyst compositions are applied to a substrate as a washcoat. Alternatively, one or more of the catalyst compositions are kneaded with other components such as fillers, binders, and reinforcing agents into an extrudable paste, which is then extruded through a die to form a honeycomb block.

Certain aspects of the present invention provide a catalytic washcoat. The washcoat comprising the copper-supported molecular sieve catalyst described herein is preferably a solution, suspension or slurry. Suitable coatings include surface coatings, coatings that penetrate a portion of the substrate, coatings that penetrate the substrate, or some combination thereof.

The washcoat may also contain non-catalytic components such as fillers, binders, stabilizers, rheology modifiers and other additives including one or more of alumina, silica, non-molecular sieve silica alumina, titania, zirconia, ceria. In certain embodiments, the catalyst composition may comprise pore formers such as graphite, cellulose, starch, polyacrylates, and polyethylenes, among others. These additional components do not necessarily catalyze the desired reaction, but rather improve the effectiveness of the catalytic material, for example by increasing its operating temperature range, increasing the contact surface area of the catalyst, increasing the adhesion of the catalyst to the substrate, and the like. In a preferred embodiment, the washcoat loading>0.3g/in³E.g. of>1.2g/in³，>1.5g/in³，>1.7g/in³Or>2.00g/in³And preferably<3.5g/in³E.g. of<2.5g/in³. In certain embodiments, the washcoat is coated at about 0.8-1.0g/in³，1.0-1.5g/in³，1.5-2.5g/in³Or 2.5-3.5g/in³Is applied to the substrate.

Preferred substrates, in particular for mobile applications, comprise so-called honeycomb bodiesA geometric flow-through monolith comprising a plurality of adjacent parallel channels open at both ends and extending generally from an inlet face to an outlet face of a substrate, produces a high surface area to volume ratio. For certain applications, it is preferred that the honeycomb flow-through monolith has a high cell density, for example, about 600 and 800 cells per square inch, and/or an average internal wall thickness of from about 0.18 to 0.35mm, preferably from about 0.20 to 0.25 mm. For certain other applications, the honeycomb flow-through monolith preferably has a low cell density of about 150-. Preferably, the honeycomb monolith is porous. In addition to cordierite, silicon carbide, silicon nitride, ceramics and metals, other materials that may be used for the substrate include aluminum nitride, silicon nitride, aluminum titanate, alpha-alumina, mullite such as acicular mullite, pollucite, heat treated cermet (thermet) such as Al₂OsZFe、Al₂O₃/Ni or B₄CZFe, or a composite material comprising fragments of any two or more thereof. Preferred materials include cordierite, silicon carbide and alumina titanate.

In certain embodiments, the present invention is a catalyst article made by the process described herein. In a particular embodiment, the catalyst article is produced by a process comprising the steps of: at the second NH₃-applying a first NH to a SCR catalyst composition, preferably before or after application as washcoat to a substrate₃-applying the SCR catalyst composition, preferably as a washcoat, to a substrate as a layer.

In certain embodiments, the second NH₃The SCR catalyst composition is located as a top layer on a substrate and another composition such as an oxidation catalyst, a reduction catalyst, a scavenger component or NO_xThe storage component is disposed as a bottom layer on the substrate.

Usually, containing the first or second NH₃Production of extruded solid bodies of SCR catalyst composition comprises blending molecular sieve and copper (separately or together as metal exchanged molecular sieve), binder, optional organic viscosity enhancing compound into a homogeneous paste, which is then addedTo the binder/matrix component or precursor thereof and optionally one or more of stabilized ceria and inorganic fibers. The mixture is compacted in a mixing or kneading device or extruder. The mixture has organic additives such as binders, pore formers, plasticizers, surfactants, lubricants, dispersants as processing aids to enhance wetting, thus producing a homogeneous batch. The shaped plastic material formed is then molded, in particular using an extrusion press or an extruder comprising an extrusion die, and the molded part formed is dried and calcined. The organic additives "burn off" during the calcination of the extruded solid body. The metal-promoted zeolite catalyst may also be washcoat or otherwise applied to the extruded solid body as one or more sublayers that are present on the surface or that are fully or partially impregnated into the extruded solid body. Alternatively, the metal-promoted zeolite may be added to the paste prior to extrusion. Preferably, the copper-supported molecular sieve is dispersed throughout the extruded catalyst body, and preferably uniformly throughout.

Extruded solid bodies containing the metal-promoted zeolites of the present invention generally comprise a unitary structure in the form of a honeycomb having uniformly sized and parallel channels extending from a first end to a second end thereof. The channel walls defining the channels are porous. Typically, an outer "skin" surrounds the plurality of channels of the extruded solid body. The extruded solid body may be formed of any desired cross-section, such as circular, square or oval. Individual channels of the plurality of channels may be square, triangular, hexagonal, circular, and the like.

The catalytic articles described herein promote the reaction of nitrogenous reductant, preferably ammonia, with nitrogen oxides to selectively form elemental nitrogen (N)₂) And water (H)₂O). Examples of such nitrogenous reducing agents include ammonia and ammonia hydrazine or any suitable ammonia precursor, such as urea ((NH)₂)₂CO), ammonium carbonate, ammonium carbamate, ammonium bicarbonate or ammonium formate. The SCR process of the present invention can achieve at least 75%, preferably at least 80%, and more preferably at least 450-At least 90% of NO_x(NO and/or NO)₂) And (4) conversion rate.

Importantly, the use of the zoned catalyst of the present invention produces low amounts of N compared to conventional SCR catalysts₂And O is a byproduct. That is, the SCR process of the present process is capable of obtaining NO-based and/or NO-based at the SCR inlet₂Low N of₂O is generated. For example, at a wide temperature range (e.g., about 150-700 deg.C, about 200-350 deg.C, about 350-550 deg.C, or about 450-550 deg.C), the inlet NO concentration at the SCR catalyst and the outlet N after the SCR catalyst₂The relative ratio of the O concentration is greater than about 25, greater than about 30 (e.g., about 30 to about 40), greater than about 50, greater than about 80, or greater than about 100. In another example, the inlet NO at the SCR catalyst can be at a wide temperature range (e.g., about 150-700 deg.C, about 200-350 deg.C, about 350-550 deg.C, or about 450-550 deg.C)₂Concentration and outlet N after SCR catalyst₂The relative ratio of the O concentration is greater than about 50, greater than about 80, or greater than about 100.

The copper-supported molecular sieve catalysts described herein in combination with an oxidation catalyst can also promote the oxidation of ammonia and limit undesirable NO by the oxidation process_xFormation (i.e., Ammonia Slip Catalyst (ASC)). In certain embodiments, the catalytic article of the present invention comprises an ASC zone at the outlet end of the substrate. In other embodiments, the ammonia slip catalyst is located on a separate block downstream of the zoned SCR catalyst. These respective blocks may be adjacent and in contact with each other, or separated by a specific distance, provided that they are in fluid communication with each other, and provided that the SCR catalyst block is located upstream of the ammonia slip catalyst block.

In certain embodiments, the SCR and/or ASC process is carried out at a temperature of at least 100 ℃. In another embodiment, the process is carried out at a temperature of from about 150 ℃ to about 750 ℃. In a specific embodiment, the temperature range is from about 175 to about 550 ℃. In another embodiment, the temperature range is 175-400 ℃. In yet another embodiment, the temperature range is 450-900 deg.C, preferably 500-750 deg.C, 500-650 deg.C, 450-550 deg.C, or 650-850 deg.C.

According to another aspect of the present invention, there is provided a method of operating a computer systemNO in raw gas_xCompound and/or oxidation of NH₃Comprising contacting the gas with a catalyst as described herein for a time sufficient to reduce NO in the gas_xLevel of compound. The method of the invention may comprise one or more of the following steps: (a) accumulating and/or combusting soot in contact with the filter inlet; (b) introducing a nitrogenous reductant into the exhaust gas stream prior to contacting the SCR catalyst, preferably without including treating the NO_xAnd an intercalated catalytic step of a reducing agent; (c) in NO_xSorbent catalyst or lean NO_xNH generation on trap₃And preferably use of such NH₃As a reductant in a downstream SCR reaction; (d) contacting the exhaust stream with a DOC to oxidize a hydrocarbon-based Soluble Organic Fraction (SOF) and/or carbon monoxide to CO₂And/or oxidation of NO to NO₂Which in turn may be used to oxidize particulate matter in the particulate filter; and/or reducing Particulate Matter (PM) in the exhaust gas; (e) contacting the exhaust gas with one or more downstream SCR catalyst devices (filters or flow-through substrates) in the presence of a reductant to reduce NO in the exhaust gas_xConcentration; and (f) contacting the exhaust gas with an ammonia slip catalyst, preferably downstream of the SCR catalyst, to oxidize most, if not all, of the ammonia and then discharge the exhaust gas to the atmosphere, or passing the exhaust gas through a recirculation loop before the exhaust gas enters/re-enters the engine.

In a preferred embodiment, the nitrogen-based reducing agent used for consumption in the SCR process, in particular NH₃May be passed through NO upstream of the SCR catalyst_xSorbent catalyst (NAC), NO lean_xTrap (LNT) or NO_xA storage/reduction catalyst (NSRC) (collectively NAC) is provided. In certain embodiments, the NAC is coated as a zoned SCR catalyst on the same flow-through substrate. In such embodiments, the NAC and SCR catalyst are coated in series, with the NAC upstream of the SCR zone.

The NAC component useful in the present invention includes a base material (e.g., an alkali metal, alkaline earth metal, or rare earth metal, including alkali metal oxides, alkaline earth metal oxides, and combinations thereof)) And a noble metal (e.g., platinum) and optionally a reducing catalyst component such as rhodium. Specific types of base materials that can be used in the NAC include cesium oxide, potassium oxide, magnesium oxide, sodium oxide, calcium oxide, strontium oxide, barium oxide, and combinations thereof. The noble metal is preferably present at about 10 to about 200g/ft³E.g. 20-60g/ft³Are present. Alternatively, the noble metal of the catalyst may be characterized by an average concentration of about 40 to about 100g/ft³。

Under certain conditions, in a periodic rich regeneration event, NH₃Can be in NO_xOn the adsorbent catalyst. NO_xSCR catalyst downstream of sorbent catalyst may improve overall system NO_xAnd (4) reducing efficiency. In a combined system, the SCR catalyst can store NH released from the NAC catalyst during a rich regeneration event₃And using stored NH₃To selectively reduce NO breakthrough through the NAC catalyst during normal lean operating conditions_xSome or all of.

In certain aspects, the present invention is a system for treating an exhaust gas produced by a combustion process, such as an exhaust gas from: internal combustion engines (whether mobile or stationary), gas turbines, coal or oil fired power plants, and the like. Such a system comprises a zoned SCR catalytic article as described herein and at least one additional component for treating an exhaust gas, wherein the zoned SCR catalytic article and the at least one additional component are designed to act as an attachment unit. The zoned SCR catalytic article and at least one additional component are optionally in fluid communication via one or more sections of a conduit for directing exhaust gas through the system.

The exhaust treatment system may include an oxidation catalyst (e.g., a Diesel Oxidation Catalyst (DOC)), which may be located upstream of the location at which the nitrogenous reductant is metered into the exhaust gas, for oxidizing nitrogen monoxide in the exhaust gas to nitrogen dioxide. In one embodiment, the oxidation catalyst is adapted to produce a gas stream, with NO and NO, entering the SCR zeolite catalyst at an exhaust gas temperature of 250 ℃ to 450 ℃ at the oxidation catalyst inlet, for example₂The volume ratio is from about 4:1 to about 1: 3. The oxidation catalyst may comprise at least oneA platinum group metal (or some combination thereof), such as platinum, palladium, or rhodium, coated on a flow-through monolith substrate. In one embodiment, the at least one platinum group metal is platinum, palladium, or a combination of both platinum and palladium. The platinum group metal may be supported on a high surface area washcoat component such as alumina, a zeolite such as an aluminosilicate zeolite, silica, non-zeolitic silica alumina, ceria, zirconia, titania or a mixed or composite oxide containing both ceria and zirconia.

The exhaust gas treatment system may comprise an additional SCR catalyst on a second flow-through monolith or wall-flow filter, wherein the second flow-through monolith or wall-flow filter containing the additional SCR is located upstream or downstream of and in fluid communication with the zoned SCR catalytic article described herein. The additional SCR catalyst is preferably a metal-exchanged zeolite, such as Cu-beta, Cu-ZSM5, Cu-CHA, Cu-ZSM-34, or Cu-AEI.

The exhaust treatment system may include an external source (e.g., an ammonia or urea injector) comprising NAC and/or nitrogen-containing reducing agent upstream of the catalytic article. The system may include a controller for catalyzing NO only when it is determined that the SCR catalyst zone is capable of catalyzing NO at or above a desired efficiency, e.g., above 100 ℃, above 150 ℃, or above 175 ℃_xDuring the reduction, an external nitrogenous reducing agent is metered into the flowing exhaust gas. The metered addition of nitrogenous reductant can be arranged so that 60% -200% of the theoretical ammonia is present in the exhaust gas entering the SCR catalyst at 1:1 NH₃NH of/NO and 4:3₃/NO₂To calculate.

The exhaust treatment system may comprise a suitable particulate filter, such as a wall-flow filter. Suitable filters include those that can be used to remove soot from the exhaust stream. The filter may be bare and passively regenerated, or may contain a soot combustion catalyst or a hydrolysis catalyst. The filter may also comprise an SCR catalyst supported on the inlet side of the filter wall, on the outlet side of the filter wall, partially or completely penetrating the filter wall, or some combination thereof. In certain embodiments, the filter is for a first filter as described hereinOr a substrate of a second catalyst zone, provided that the alternating zones are located on the flow-through substrate. For example, a wall-flow filter may be used as the substrate for the first zone, and a flow-through honeycomb may be used as the substrate for the second zone. In another example, a flow-through honeycomb may be used as the substrate for the first zone and a wall-flow filter may be used as the substrate for the second zone. In such embodiments, the wall flow substrate may further comprise NH₃The catalyst is oxidized to form an ASC zone.

The filter may be located in the exhaust treatment system upstream or downstream of the zoned SCR catalyst. Preferably, if a DOC is present, the filter is located downstream of the DOC. For embodiments comprising a bare filter (i.e., without a catalyst coating) and an ammonia injector upstream of a zoned SCR catalyst, the injector may be located upstream or downstream of the filter, provided that it is located upstream of the zoned SCR catalyst. For embodiments having a filter containing a hydrolysis catalyst and a downstream zoned SCR catalyst, the ammonia injector is preferably located upstream of the filter.

Referring to fig. 11, an exhaust treatment system is shown comprising an internal combustion engine 501, an exhaust treatment system 502, direction 1 of exhaust flow through the directing system, an optional DOC 510 and/or optional NAC 520, an optional particulate filter 570, an optional external source of ammonia and injector 530, a zoned SCR catalyst 540, an optional additional SCR catalyst 550, and an optional ASC 560.

The methods described herein for treating exhaust gas may be performed on exhaust gas derived from a combustion process, such as from an internal combustion engine (mobile or stationary), a gas turbine, and a coal or oil fired power plant. The process can also be used to treat gases from industrial processes such as refining, stripping from refinery heaters and boilers, furnaces, chemical industry, coke ovens, municipal wastewater treatment plants and incinerators, and the like. In one embodiment, the method is used to treat exhaust gas from a vehicular lean-burn internal combustion engine, such as a diesel engine, a lean-burn gasoline engine, or an engine powered with liquefied petroleum gas or natural gas.

Claims

1. A catalytic article, comprising:

b. a first catalytic zone consisting of a first washcoat,

d. a third catalytic zone consisting of a second washcoat layer, and

2. The catalytic article of claim 1, wherein the first washcoat layer comprises a first NH₃-SCR catalyst composition, said first NH₃-the SCR catalyst comprises a first copper supported molecular sieve having a copper to aluminum atomic ratio of 0.1 to 0.375.

3. The catalytic article of claim 1, wherein the second washcoat layer comprises a second NH₃-SCR catalyst composition, the second NH₃-the SCR catalyst comprises a second copper supported molecular sieve having a copper to aluminum atomic ratio of 0.3 to 0.6.

4. The catalytic article of claim 1, wherein the first catalytic region has a ratio of Cu to Al that is less than the ratio of Cu to Al of the second catalytic region.

5. The catalytic article of claim 1, wherein the first copper-supported molecular sieve has a lower copper concentration than the second copper-supported molecular sieve.

6. The catalytic article of claim 1, wherein the copper loading of the first copper-loaded molecular sieve is 50-90% of the second copper-loaded molecular sieve.

7. The catalytic article of claim 1, wherein the first copper-supported molecular sieve has a first SAR and the second copper-supported molecular sieve has a second SAR that is greater than the first SAR.

8. The catalytic article of claim 1, wherein the first molecular sieve is an aluminosilicate having a SAR of 10-20 and the second molecular sieve is an aluminosilicate having a SAR of 20-50.

9. The catalytic article of claim 1, wherein the first and second molecular sieves have a small pore framework.

10. The catalytic article of claim 1, wherein the first and second molecular sieves have a CHA framework.

11. A system for treating an exhaust gas, comprising:

a. the catalytic article of claim 1; and

wherein the catalytic article of claim 1 and the one or more exhaust treatment components are in fluid communication and are in series.

12. A method for treating exhaust gas, comprising:

so as to contain NO_xAnd NH₃With the catalytic article of claim 1;

adding NO_xIs selectively reduced to N₂And H₂O。